In cathode ray tube displays, such as oscilloscopes and alphanumeric display devices, the intensity of the display on the face of the cathode ray tube is controlled by means of a manual control that supplies a DC intensity level signal to the cathode ray tube. A modulation signal, which may be for example pulses for producing alphanumeric displays, is also supplied to the tube for producing the display. In these types of displays it is necessary to supply control signals lying in a range from DC through several megahertz. Such a range is difficult to provide without producing glitches and/or breaks in the continuity, which means that all signals will not be applied equally. Further, relatively high voltages are required on the cathode ray tube to control the intensity and it is undesirable that these high voltages be available at the manual control.
In prior art devices a DC restoration circuit employing rectifier diodes, a tapped high voltage transformer and coupling capacitors were generally required to provide the function of supplying AC and DC intensity control signals to a cathode ray tube. AC control signals are generally supplied to the cathode of the tube and the DC and lower frequency control signals are applied to the grid with a rectifier diode connected therebetween. In such circuits it is difficult to provide wide bandwidth operation along with the required response at all frequencies so that no glitches appear in the bandwidth. Further, the transformer supplies a large AC voltage and in turn generates a large amount of noise and interference which is detrimental to nearby noise-sensitive circuits.